Housing and enclosures for storing and protecting electronics and electronic products are well known. In some applications, and in particular with more powerful and compact electronics, the electronic enclosures must shield the electronics or electronic products from electromagnetic interference (EMI) and/or radio frequency interference (RFI), prevent significant amounts of EMI or RFI from radiating from the enclosure, and/or provide internal circuit-to-circuit shielding. The enclosures are also typically environmentally sealed around the periphery and can provide thermal transfer from the electronic product to the surrounding ambient or between circuit-to-circuit.
In the past, electronic enclosures have been formed from metal to meet emissions and radiated noise requirements. The metal enclosures, however, have certain disadvantages in being costly and weighty, are limited in design and manufacturing possibilities, and can have issues with respect to deflection, humidity and expansion over a broad temperature range.
As such, plastic (such as thermoplastic) enclosures have received acceptance in the market place as meeting certain of the needs of electronic product manufacturers. However, these enclosures, being non-conductive, require some sort of shielding to meet emissions and radiated noise requirements. Typical shielding technologies for plastic enclosures have included coatings of copper, silver or nickel; vacuum metallization; and plating-on-plastics, among others. The coatings are applied across the major surface portions of the enclosures. Examples of this kind of technology are shown in U.S. Pat. Nos. 4,227,037; 4,435,465; 4,777,565 and 5,311,408.
Another shielding technology has included applying a shielding assembly to the inside surface of the enclosure. The shielding assembly comprises a pair of porous non-woven layers, one of which consists of uniform fibers of a solder-like metal alloy with a low melting temperature, and the other which consists of an EVA polymer that functions as a hot melt adhesive. The adhesive side of the assembly is located against the inside surface of the enclosure. Upon heating, the shielding assembly becomes a fused metal coating with the enclosure. This technology is available from the 3M Corporation.
At the interface locations between a cover and the underlying enclosure or between the cover and the electronic product, it is necessary to have a resilient type of shielding material. A resilient type of shielding material enables the cover to be repeatably removed and replaced on the enclosure while maintaining constant and maximum area of contact for shield continuity, environmental sealing and/or thermal transfer. The coatings, metallizations and plating-on-plastics can have certain limitations for these locations. Specifically, these technologies can be too thin and not resilient (conformable) enough to provide an appropriate gasket-like response at the interface locations. The shielding assembly with the EVA polymer and metal alloy also suffers from these limitations. As such, at the interface locations, a separate resilient type of conductive gasket has typically been used. One type of gasket material appropriate for the interface locations is available from the Chomerics Division of Parker-Hannifin Corporation under the trademark CHO-SEAL. Such gasket material technology is also shown in U.S. Pat. Nos. 4,545,926 and 4,780,575.
While the combination of the technologies described above has been used to provide an overall shielding solution for electronic enclosures, the combination of the two technologies requires separate compounds for the gasket and the major surface portions of the enclosure. Using separate compounds, however, can increase material costs. The technologies also require separate manufacturing steps, which increases labor costs and manufacturing complexity. Further, the coatings, metallization or plating for the cover and/or gasket must sometimes be applied by an outside vendor, which further can increase the overall cost of the enclosure.
As such, it is believed that there is a demand in the industry for a single shielding solution which provides i) an effective EMI/RFI shield across the entire cover plate and between internal chambers for circuit-to-circuit shielding, and ii) a gasket-type resiliency at the interface locations between the cover plate and the electronics enclosure or the electronic product for environmental sealing, thermal transfer and shield continuity. It is desirable that the shielding solution be easy to apply, and reduce manufacturing complexities and costs.